In general, oil content in wastewater has severe effects on the environment, and makes it much more difficult to reclaim such type of water.
Use of adsorbents is known in the art as a solution to remove oil content from wastewater, and among the commonly used adsorbents is activated carbon; however, it is quickly poisoned and is thus impractical in treating large volumes.
The use of oil shale ash is also reported as an effective means for adsorbing oil content in wastewater, as disclosed in the scientific article M. Aljaradin, “Comparison of Retort Water Treatment Methods—A Case Study in Jordan,” Journal of Water Management and Research, 68: pp. 37-41, Lund 2012.
However, the use of oil shale ash renders the treated water turbid, and can introduce metal ions to the treated water, thus causing other problems that must then be resolved. Also, when oil shale ash is wetted, it forms a sludge that blocks the passage of water, which prevents it from being used in column filters.